Method of recovering sodium hydroxide from alkaline wash liquors



, Novi W. H. FURN'ESS y METHOD OF RECOVERING SODIUM HYDROXIDE FROM ALKALINE WASH LIQUORS Filed May 1s. 1940 #man rfa/f 000 PULP INVENTOR A ATTORNEYS ,possible to employ a Patented Nov. 3, 1942 "METHOD or` nEcovEalNG sonnJM HY- Daoxma FROM LIQUORfS ALKALINE WASH william n. Furness, neadenneid, N. J., as

signor to American Rayon Company', Inc

Riverton, N. J., a corporation of New J ersey, Application May 13, 1940, serial No. 334,894

4 Claims.

This invention relates to a method of recovering sodium hydroxide from alkaline liquors, and it is particularly useful in the recovery ofi caustic vsodal from the alkaline wash liquors of theI cuprammonium process of manufacturing rayon,

lms, staple vand the like, vof my copending application Serial No. 332,694, filed May 1, 1940.

`In that process the freshly spun material is at one stage subjected to a water wash to remove caustic 'soda copper and ammonia therefrom. The washv liquor additionally contains sodium sul-` phate and sodium carbonate derived from the system. 1

The accompanyingl drawing is a flow-sheet, illustrating diagrammatically a system which includes the preferred cycle of my invention.

The copper is insoluble and can bereadily removed from the wash liquor by filtration, seta tling or the like.y The ammonia is removed lby heating. Caustic'soda and sodium sulphates and carbonates remain behind in the solution. In

T- addition to driving off-ammonia, the heating inr creases the concentration of the chemicals in the wash liqor, and is continued until a 'concentration effective for recovery is obtained. l

The amount" of sulphates and carbonates is A, `nowdetermined and to the concentrated liquor,

while still hot, is added an equivalent amount of barium hydroxide in solution.- It is undesirable to have any excess of barium hydroxide in order to avoid carryover.` In fact, it is best to err on the safe side'and use slightly less than the theoretical equivalent amount of barium hydroxide.

The barium hydroxide leaves the caustic soda in the liquor unaected, but reacts with the suly phates and. carbonatesto form` additional caustic soda and also barium carbonate and barium sul phate. 'Ihe reactions eral lines': l

NazSO4+Ba(OH)'z=2NaOH+BaSO4 NazCOn-i-BMOH) a=2NaOPl+BaCOs The barium carbonate and barium sulphate are insolubleand precipitate.

The barium hydroxide solution is added to 'the proceed along the gen- "hot liquor in hot condition in order to obtain a dense precipitate which will fall out in a few moments. liurtherxtoore.'` since barium hydroxide has low solubility in cold water, the barium hydroxide solution should be hot in order tomake it A concentrated solution thereof.` l j v Theprecipitated barium sulphates and car.-

containing the sodium hydroxide, as for example by decanting, filtering or the like.

The separated barium-sulphate and carbonate can be readily washed, after which a small amount of sulphuric acid is addedto convert the carbonate into barium sulphate, the reaction being substantially:

V The barium sulphate is now burned or roasted with carbon to form barium sulphide, about 156o C. being required. The barium sulphide is now leached from the carbon withhot Water and to the barium sulphide solution thus obtained is added cupric oxide, in equivalentvamount. The y solution is now boiled, producing cupric sulphide and barium hydroxide. These are separated and the barium hydroxide is utilized to treat some additional alkaline wash liquor.

The cupric sulphide is now burned or yroasted in the same manner as pyrites, which producesv cupric oxide` and sulphur dioxide.-

'I'he cupric oxide thusproduced is utilized to convert some additional barium sulphide into barium hydroxide. The sulphur dioxide obtained is usable in the manufacture of wood pulp.

The causticl soda solution obtained by the process may be advantageously used in various ways, depending upon its concentration.- For example, it may be used to fortify the setting bath,

or it may be used in the preparation of cellulosic spinning solution (goo).

I claim: l

1. A cyclic process of recovering and reusing treating agentsV and materials of a wash liquor used in the cuprammonium methodi'of manufacturing rayon. lms, staple and the like, whichv wash liquor contains water, caustic soda, sodium sulphate and sodium carbonate, including the steps which comprise: (a) adding barium hydroxide tothe liquor to convert sodium sulphate: and

t sodiumV carbonate to barium sulphate, barium carbonate and caustic soda; (b) separating the barium sulphateand carbonate from the liquor,

which liquor then comprises a caustic soda solution adapted for reuse in said cuprammonium method; (c) adding sulphuric acid to the barium sulphate and; carbonate to convert thecarbonate l to sulphate; (d) burning the barium sulphate with carbon to convert the sulphate to sulphide;

(e) separating, the carbonfrom the bariumy sul--l plaide and dissolvm the -suipmde in watergm adding cupric oxide and boilingthe solution to j bonatescan be readlv separated from the liquor form cupric sulphide and barium hydroxide; and

(g) separating the cupric sulphide and barium lrvdroxide, and reusing the barium hydroxide in step (a).

2. A process in accordance with claim 1 and further including the following steps: (h) burning the cupric sulphide to vform cupric oxide and sulphur dioxide; and (i) separating the cupric oxide and sulphur dioxide, and reusing the cupric oxide in Step 3. A process in accordance with claim 1 in 10 l which the quantity of barium hydroidde added in step (a) is 1n the neighborhood of but not above the theoretical amount required to convert the sodium sulphate and sodium carbonate.

4. A process in accordance with claim 1 in which step (a) is effected by dissolving the barium hydroxide in water and mixing the solution with the liquor while both are heated.

WIuIAM H. FUaNnss. 

